Final answer:
The distribution of solutes across membranes is determined by the concentration gradient, and active transport processes are not exclusively dictated by solute size. Diffusion leads to a dynamic equilibrium where solute distribution becomes even, and osmosis describes the movement of water in response to solute concentration gradients.
Step-by-step explanation:
The distribution of solutes across membranes depends on the concentration gradient.
The equiLibrium distribution of solutes across a semipermeable membrane like the cell membrane is significantly influenced by the concentration gradient. In a process known as diffusion, solutes move from regions of higher concentration to regions where they are less concentrated, until dynamic equilibrium is achieved. At this point, though individual molecules continue to cross the membrane, there is no net movement because the rates of diffusion in both directions become equal. Factors such as the extent of the concentration gradient and the mass of the diffusing molecules affect the rate at which equilibrium is reached. Osmosis is a special case of diffusion where water, being able to readily traverse most membranes through aquaporins, moves across the membrane toward the side with a higher solute concentration, also seeking equilibrium.
Osmosis, which is the diffusion of water across a semipermeable membrane, also depends on the concentration gradient. Water will move from an area of higher concentration to an area of lower concentration until equilibrium is reached.
The distribution of solutes across membranes is not determined by the size of the solute molecules, but rather by the concentration gradient.